[NaCl SDK] Set "recommended" tag to "yes" automatically for stable pepper bundle.

native_client_sdk/src/build_tools/json/naclsdk_manifest2.json

 {
   "bundles": [
     {
       "name": "sdk_tools",
       "description": "Native Client SDK Tools, revision 134553",
       "stability": "stable",
       "recommended": "yes",
       "version": 1,
       "archives": [
         {
@@ skipping 140 matching lines @@
           },
           "host_os": "win",
           "size": 108888118
         }
       ],
       "revision": 124253
     },
     {
       "name": "pepper_19",
       "description": "Chrome 19 bundle, revision 129248",
-      "stability": "stable",
-      "recommended": "yes",
+      "stability": "post_stable",
+      "recommended": "no",
       "version": 19,
       "repath": "pepper_19",
       "archives": [
         {
           "url": "https://commondatastorage.googleapis.com/nativeclient-mirror/nacl/nacl_sdk/19.0.1084.33/naclsdk_mac.bz2",
           "checksum": {
             "sha1": "b39038bf3775c6db907c6b99d722b5dac37f6e50"
           },
           "host_os": "mac",
           "size": 117551214
@@ skipping 13 matching lines @@
           },
           "host_os": "win",
           "size": 113168433
         }
       ],
       "revision": 129248
     },
     {
       "name": "pepper_20",
       "description": "Chrome 20 bundle, revision xxxxx",
-      "stability": "beta",
-      "recommended": "no",
+      "stability": "stable",
+      "recommended": "yes",
       "version": 20,
       "repath": "pepper_20",
       "archives": [],
       "revision": 0
     },
     {
       "name": "pepper_21",
       "description": "Chrome 21 bundle, revision xxxxx",
-      "stability": "dev",
+      "stability": "beta",
       "recommended": "no",
       "version": 21,
       "repath": "pepper_21",
       "archives": [],
       "revision": 0
     },
     {
       "name": "pepper_canary",
       "description": "Chrome Canary",
       "stability": "canary",
       "recommended": "no",
       "version": 0,
       "repath": "",
       "archives": [],
       "revision": 0
     }
   ],
   "manifest_version": 2
 }